I use max and sketchup, it take me days to understand that i have to bring order in the material browser before exporting, i guess it is the same way in Blender, also the outpout options in the ase exporter, here's one model i'm currently working on and the six materials that are going to be display in unrealed SM browser, it's a need to add somes smoothing groups for not having lighting issues when building the map afterward .

That building is cool. Nice work. It's funny how it's harder to make stuff in ruins than it is to make them normal.

I'm not sure what you mean about bringing order in the material browser. I'm very new to this. I know a lot of terms but I am still learning what they mean. For the sign I just did the minimum. Two materials with one texture assigned to each material and the different materials assigned to different faces on the mesh. It could maybe use some specularity but I think it's fine for now. I'll look into smoothing groups though. There is still a lot for me to learn if I want to make any assets for the game besides a simple sign. I'm making some sci-fi panels that I plan on using to learn about materials.